Regeneration of the Central Nervous System of mammals was formerly thought to be abortive. However, there is a cyclic turnover of synaptic complexes in number and morphological type, rostral to a spinal cord lesion. Although the ventral horn motoneuron is chronically denervated after spinal cord hemisection the new synaptic complexes that are formed show that new sources of presynaptic boutons are available. Protein synthetic inhibitors modify the pathological response of deafferented motoneurons which may result in the growth of the new source of presynaptic boutons into the cicatrix.